The problem on which the present disclosure is based will be explained on the basis of the energy and data transfer between a terminal side with a transmitter and a sensor side with a sensor.
Generally, a cable is connected to a transmitter in order to connect it to a sensor. The connection between the cable and the sensor often takes place via a plug-in connection, by means of, for example, galvanically decoupled—in particular, inductive—interfaces. In this way, electrical signals may be transmitted in a contactless manner. As a result of this galvanic isolation, advantages are seen with respect to corrosion protection, potential isolation, prevention of mechanical wear and tear of the connectors, etc. The applicant sells such systems under the designation “Memosens”. Other similar designs are, for example, “Memosens” from the company Knick, “ISM” from Mettler-Toledo, the “ARC” system from Hamilton and “SMARTSENS” from Krohne.
The aforementioned inductive interfaces are generally realized as a system with two coils which are plugged into one another by means of the aforementioned plug-in connection, for example. Typically, both data (in both directions) and energy (from the terminal side to the sensor side) are transmitted. In doing so, the energy must be high enough to provide the connected sensor with sufficient energy and thus ensure a long-term measurement operation.
The challenge presented by such contactless energy and data transfer consists in the rough operating and environmental conditions in the industrial environment. This requirement has the effect that the tolerance ranges for the components (inductances of the coils, etc.) that must be specified as a result of the environmental conditions (temperature, air humidity, etc.) are particularly broad. Temperature ranges of −20° C. up to 135° C. occur. If assemblies are, for example, designed for typical temperatures at which medical devices are sterilized (typically above 120° C.), then significantly modified inductance values must, for example, be expected at high temperatures for the coils used in these assemblies.
With respect to the tolerances, what is particularly to be pointed out is the coupling transformer, which inductively couples the coil on the terminal side with the coil on the sensor side or forms a transformer with these two coupled coils. In this coupling system, the mechanical pairing of the two partner coils is decisive, and a wide dispersion of the inductive coupling may result in problems with respect to the transmission behavior.
One possibility for solving the problem consists in adjusting the power transmitted from the terminal side to the sensor side, such that the sensor is supplied with sufficient power under all environmental conditions and interferences. This may, however, result in the maximum permissible total power consumption being exceeded. In addition, too much power that is not necessary is often transmitted.
Another possibility for solving the problem includes, additionally, an element for temperature compensation. In this way, the temperature behavior of the inductive coupling may be compensated. The stability of the sensor-side power supply is thus improved. Still, this measure cannot counteract all environmental conditions and interferences. It may also occur in this case that the total power is exceeded if the sensor load is too high.
With another possibility for solving the problem, the power consumption of the inductive coupling is determined on the terminal side, and, subsequently, the coupling is regulated to a corresponding target value. With this method, the total power consumption of the inductive coupling can be kept constant. The power delivered to the sensor can, however, still fluctuate, depending upon the type of sensor, and also under the aforementioned environmental conditions and interferences.
None of the solutions mentioned can, however, keep the power provided to the sensor constant through all environmental conditions and interferences. In part, significant energy reserves must be provided, which are then not available for the actual purpose—namely, the sensing of the measured value—of the sensor electronics. Furthermore, it cannot be ensured that the power provided on the terminal side is also actually available to the sensor. All known and aforementioned topologies are unable to provide the sensor with the power it really needs. The specific need of the sensor, considering all the disturbance variables, is not taken into account.